Input: ti_am335x_tsc - set ADCREFM for X configuration

Input: ti_am335x_tsc - set ADCREFM for X configuration

As reported by the STEPCONFIG[1-16] registered field descriptions of the
TI reference manual, for the ADC "in single ended, SEL_INM_SWC_3_0 must
be 1xxx".

Unlike the Y and Z coordinates, this bit has not been set for the step
configuration registers used to sample the X coordinate.

Fixes: 1b8be32e6914 ("Input: add support for TI Touchscreen controller")
Signed-off-by: Dario Binacchi <dariobin@libero.it>
Link: https://lore.kernel.org/r/20211212125358.14416-2-dariobin@libero.it
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>